Buggy code:
public class Form < T > extends WebMarkupContainer implements IHeaderContributor , IFormSubmitListener { private static final String HIDDEN_DIV_START = "<div<seq2seq4repair_space>style=\"width:0px;height:0px;position:absolute;left:-100px;top:-100px;overflow:hidden\">" ; public abstract static class ValidationVisitor implements IVisitor < FormComponent < ? > , Void > { public void component ( final FormComponent < ? > formComponent , final IVisit < Void > visit ) { } public abstract void validate ( FormComponent < ? > formComponent ) { } } private static class FormModelUpdateVisitor implements IVisitor < Component , Void > { private final Form < ? > formFilter ; public FormModelUpdateVisitor ( Form < ? > formFilter ) { } public void component ( final Component component , final IVisit < Void > visit ) { } } public static final String METHOD_GET = "get" ; public static final String METHOD_POST = "post" ; private static final short FLAG_SUBMITTED = FLAG_RESERVED1 ; private static final Logger log = LoggerFactory . getLogger ( Form . class ) ; private static final long serialVersionUID = 1L ; private static final String UPLOAD_FAILED_RESOURCE_KEY = "uploadFailed" ; private static final String UPLOAD_TOO_LARGE_RESOURCE_KEY = "uploadTooLarge" ; private IFormSubmittingComponent defaultSubmittingComponent ; private Bytes maxSize = null ; private short multiPart = 0 ; private static final short MULTIPART_HARD = 1 ; private static final short MULTIPART_HINT = 2 ; public Form ( final String id ) { } public Form ( final String id , IModel < T > model ) { } public void add ( IFormValidator validator ) { } public void remove ( IFormValidator validator ) { } public final void clearInput ( ) { } public final void error ( String error , Map < String , Object > args ) { } public final IFormSubmitter findSubmittingButton ( ) { } public final IFormSubmittingComponent getDefaultButton ( ) { } public final Collection < IFormValidator > getFormValidators ( ) { } public final CharSequence getJsForInterfaceUrl ( CharSequence url ) { } public final Bytes getMaxSize ( ) { } public Form < ? > getRootForm ( ) { } public String getValidatorKeyPrefix ( ) { } public final boolean hasError ( ) { } public boolean isRootForm ( ) { } public final boolean isSubmitted ( ) { } @ Override public boolean isVersioned ( ) { } public final void onFormSubmitted ( ) { } public final void onFormSubmitted ( IFormSubmitter submitter ) { } public void process ( IFormSubmitter submittingComponent ) { } private void callOnError ( IFormSubmitter submitter ) { } private void markFormsSubmitted ( ) { } public final void setDefaultButton ( IFormSubmittingComponent submittingComponent ) { } public final void setMaxSize ( final Bytes maxSize ) { } public void setMultiPart ( boolean multiPart ) { } @ Override public final Component setVersioned ( final boolean isVersioned ) { } public final < R > R visitFormComponents ( final IVisitor < ? extends FormComponent < ? > , R > visitor ) { } public final < R > R visitFormComponentsPostOrder ( final IVisitor < ? extends FormComponent < ? > , R > visitor ) { } private boolean anyFormComponentError ( ) { } private void dispatchEvent ( final Page page , final String url ) { } private void inputChanged ( ) { } protected void appendDefaultButtonField ( final MarkupStream markupStream , final ComponentTag openTag ) { } protected void beforeUpdateFormComponentModels ( ) { } protected void delegateSubmit ( IFormSubmitter submittingComponent ) { } public final String getHiddenFieldId ( ) { } protected String getMethod ( ) { } @ Override protected boolean getStatelessHint ( ) { } public boolean isMultiPart ( ) { } protected boolean handleMultiPart ( ) { } protected void onFileUploadException ( final FileUploadException e , final Map < String , Object > model ) { } @ Override protected void internalOnModelChanged ( ) { } protected final void markFormComponentsInvalid ( ) { } protected final void markFormComponentsValid ( ) { } private void markNestedFormComponentsValid ( ) { } private void internalMarkFormComponentsValid ( ) { } @ Override protected void onComponentTag ( final ComponentTag tag ) { super . onComponentTag ( tag ) ; checkComponentTag ( tag , "form" ) ; if ( isRootForm ( ) ) { String method = getMethod ( ) . toLowerCase ( ) ; tag . put ( "method" , method ) ; String url = getActionUrl ( ) . toString ( ) ; if ( encodeUrlInHiddenFields ( ) ) { int i = url . indexOf ( '?' ) ; String action = ( i > ( - 1 ) ) ? url . substring ( 0 , i ) : "" ; tag . put ( "action" , action ) ; } else { <START_BUG> tag . put ( "action" , Strings . escapeMarkup ( url ) ) ; <END_BUG> } if ( isMultiPart ( ) ) { tag . put ( "enctype" , "multipart//form-data" ) ; tag . put ( "accept-encoding" , Form . getApplication ( ) . getRequestCycleSettings ( ) . getResponseRequestEncoding ( ) ) ; } else { String enctype = ( ( String ) ( tag . getAttributes ( ) . get ( "enctype" ) ) ) ; if ( "multipart//form-data" . equalsIgnoreCase ( enctype ) ) { setMultiPart ( true ) ; } } } else { tag . setName ( "div" ) ; tag . remove ( "method" ) ; tag . remove ( "action" ) ; tag . remove ( "enctype" ) ; } } protected CharSequence getActionUrl ( ) { } @ Override protected void renderPlaceholderTag ( ComponentTag tag , Response response ) { } protected boolean encodeUrlInHiddenFields ( ) { } @ Override protected void onComponentTagBody ( final MarkupStream markupStream , final ComponentTag openTag ) { } protected void writeParamsAsHiddenFields ( String [ ] params , AppendingStringBuffer buffer ) { } private String recode ( String s ) { } @ Override protected void onDetach ( ) { } protected void onError ( ) { } @ Override protected void onBeforeRender ( ) { } protected void onSubmit ( ) { } protected final void updateFormComponentModels ( ) { }

Fix:
tag . put ( "action" , url ) ;